1. Field of the Invention
The present invention relates to a sensor chip and a photoelectric conversion apparatus using the same and, more particularly, to a multichip photoelectric conversion apparatus using an array of a plurality of sensor chips.
2. Related Background Art
Conventionally, a photoelectric conversion apparatus (linear image sensor) in which light-receiving elements are arranged in a line has been widely used in an image reading apparatus such as a facsimile, a digital copying machine, and a scanner.
Since a sensor chip for use in a linear image sensor is generally made from a silicon wafer, the sensor length is limited by the wafer size. Therefore, it is difficult to manufacture a linear image sensor chip having a length identical to the width of an original to be read having a general size. For this reason, in order to use a single sensor chip, an imaging optical system is used to image an original to be read on the sensor chip in a reduced scale, thereby reading an image carried by the original. An apparatus utilizing such a reduction imaging optical system, however, requires a space for the optical system. Therefore, it is difficult to make the apparatus compact. In addition, it is difficult to obtain a sufficient resolution.
For this reason, a so-called multichip image sensor in which a plurality of linear image sensor chips are linearly arranged has been put into practical use.
FIG. 1 is a block diagram showing an arrangement of a conventional multichip image sensor.
Referring to FIG. 1, n light-receiving elements 2-1-1 to 2-1-n are formed in a line in the x direction on a sensor chip 1-1. A circuit 3-1 for sequentially selecting outputs from the light-receiving elements 2-1-1 to 2-1-n is formed on the chip 1-1. An amplifier 4-1 for amplifying an output from the circuit 3-1 is also formed on the chip 1-1. An output from the amplifier 4-1 is output outside the chip from an output line 5-1 generally via a signal extracting section.
The circuit 3-1 is driven by an external driver via an input line 8-1.
Sensor chips 1-2 to 1-m have the same arrangement as that of the sensor chip 1-1. In the sensor chips 1-2 to 1-m, therefore, the same reference numerals as in the sensor chip 1-1 denote the same parts.
The sensor chips 1-1 to 1-m are arranged in a line in the x direction. Therefore, a total of (n.times.m) light-receiving elements are arranged in a line in the x direction. Upon image reading, an original carrying an image to be read and/or a photoelectric conversion apparatus are conveyed in the y direction relative to each other so that the original faces the light-receiving elements.
Outputs from all light-receiving elements of the chip 1-1 are sequentially selected by the circuit 3-1 and externally output from the output line 5-1. Outputs from all light-receiving elements of the chip 1-2 are then sequentially selected by a circuit 3-2 and externally output from an output line 5-2. Subsequently, signals from light-receiving elements are similarly, sequentially read. As a result, outputs from all light-receiving elements are time-serially output.
In the conventional multichip image sensor as described above, since an output signal from each sensor chip is independently extracted to an external signal processor, the number of signal lines is increased to complicate the wiring. In order to solve this problem, a common signal line may be used to extract signals to the external signal processor. If, however, all sensor chips including those not externally outputting signals from light-receiving elements are connected to the output line, crosstalk between signals easily occurs to reduce an S/N ratio of a read signal.
In addition, in the above conventional multichip image sensor, an amplifier is in an operative state even while light-emitting elements of each chip do not externally output signals. For this reason, if the number of sensor chips is increased, unnecessary power consumption is increased or heat is generated to increase the chip temperature, thereby degrading the sensor characteristics.